This subcontract of the Adolescent Health Survey investigates adolescent health behaviors using behavior genetic methods to separate genetic from environmental influences. Environmental influences are further separated into environmental variance caused by shared environment (e.g., makes siblings alike) and into that caused by nonshared environment (e.g., makes siblings different). Specific, measured environmental mechanisms and processes also will be investigated. The behavior genetic sample consists of same-sex kinship pairs; namely, identical twins, fraternal twins, half- siblings, and unrelated children reared together, and of all three categories (M-M, F-F, and F-M) of biological full siblings. Excluding full siblings, the size of this sample is 500 pairs of each type (2,000 sibling pairs or 4,000 individuals). The number of full sibling pairs will exceed 250 sibling pairs per category. It is hypothesized that two health-related measures, sexual experience and problem behavior, will have a substantial shared environmental variance component. The shared variance component is expected to increase for siblings in overlapping peer groups. community characteristics (e.g., % divorced) are expected to mediate the shared environmental effect on these outcomes. Physical health behaviors are expected to be highly heritable with little shared environmental variance. Environmental contextual effects on pubertal development (Belsky hypothesis) will be evaluated. Covariation among IQ, non- intellectual personality traits, and adolescent health behaviors will be apportioned to the composite variance components. It is hypothesized that the genetic component is a major source of this covariation.